Purification and Amino Acid Sequence of Kunitz-Type Protease Inhibitor Found in the Hemocytes of Horseshoe Crab (Tachypleus tridentatus)

抄録

A low molecular weight protein protease inhibitor was purified from Japanese horseshoe crab (Tachypleus tridentatus) hemocytes. It consisted of a single polypeptide with a total of 61 amino acid residues. This protease inhibitor inhibited stoichiometrically the amidase activity of trypsin (K₁=4.60×10^-10M), and also had inhibitory effects on α-chymotrypsin (K₁=5.54α10^-9M), elastase (K₁=7.20α10^-8M), plasmin, and plasma kallikrein. However, it had no effect on T. tridentatus clotting enzyme and factor _??_, mammalian blood coagulation factors (activated protein C, factor Xa and a-thrombin), papain, and thermolysin. The complete amino acid sequence of this inhibitor was determined and its sequence was compared with those of bovine pancreatic trypsin inhibitor (BPTI) and other Kunitz-type inhibitors. It was found that the amino acid sequence of this inhibitor has a high homology of 47 and 43% with those of sea anemone inhibitor 5-II and BPTI, respectively. Thus, this protease inhibitor appeared to be one of the typical Kunitz-type protease inhibitors.